CDC surveillance data show influenza activity higher than typical for early November, with Washington state public health laboratories confirming two new H5 infections.

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Seasonal influenza activity continues to rise across much of the US and is higher than normally seen at this time of year, according to the Centers for Disease Control and Prevention’s (CDC) latest weekly surveillance report. Clinical laboratories reported 9.1% of respiratory specimens testing positive for influenza during the week ending Oct 31.

Clinical laboratories tested 51,351 specimens that week, and 4,696 were positive. Cumulative positivity since Oct 4 stands at 6.8% of 233,110 specimens tested. Influenza A accounted for 98.6% of positive clinical lab specimens. Positivity rose nationally and in most regions. It held stable in region 7 and fell in region 9, which CDC says could reflect incomplete reporting.

CDC cautioned that an earlier rise in activity does not necessarily lead to a higher seasonal peak or greater overall severity. All data are preliminary.

H1N1 Predominates in Public Health Lab Data

Of the 513 influenza-positive specimens reported by public health laboratories, 502 were influenza A and 11 were influenza B. Among the 388 influenza A viruses that were subtyped, 379 (97.7%) were A(H1N1)pdm09, 7 (1.8%) were A(H3N2), and 2 (0.5%) were A(H5). Since late May, 83.4% of reported influenza A viruses have been A(H1N1)pdm09, most of them in the D.3.1.1 HA subclade.

CDC noted that recently circulating D.3.1.1 viruses have split into distinct groups with different genetic changes in their HA genes, and the agency is seeing more genetic diversity among co-circulating A(H1N1)pdm09 viruses than before. The agency said it is too early to know which viruses will predominate or whether there are implications for vaccine effectiveness this season.

Among the 688 influenza viruses CDC has genetically characterized since May 24, 486 were A(H1N1)pdm09, 106 were A(H3N2), and 96 were B/Victoria. Of the A(H3N2) viruses, 101 (95.3%) belonged to subclade K.

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Vaccine Match and Antiviral Susceptibility

CDC’s antigenic testing found most characterized viruses are well recognized by antisera raised against the 2026-2027 Northern Hemisphere vaccine reference viruses:

• A(H1N1)pdm09: 140 of 147 viruses (95.2%) were well recognized by antisera to the A/Missouri/11/2025-like reference virus.
• A(H3N2): all 35 viruses were well recognized by antisera to the A/Darwin/1415/2025-like reference virus.
• B/Victoria: all 33 viruses were well recognized by antisera to the B/Pennsylvania/14/2025-like reference virus.

On antiviral susceptibility, 8 of 654 viruses tested (1.2%) showed reduced inhibition by oseltamivir. All were A(H1N1)pdm09 viruses carrying the NA-I223V and NA-S247N substitutions. No viruses showed reduced inhibition by peramivir or zanamivir, and none showed decreased susceptibility to baloxavir.

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Two New H5 Infections in Washington

CDC reported two confirmed human infections with avian influenza A(H5) virus, including one death. The Washington State Department of Health reported both cases in adults who worked at commercial dairy cattle farms where highly pathogenic avian influenza A(H5N1) has been detected in cows.

The first patient developed respiratory symptoms during the week ending October 24, went to an emergency department the following week, was hospitalized, and died. The testing pathway involved several laboratories. A specimen collected at the health care facility was presumptive positive for influenza A(H5) at the University of Washington, then confirmed at the Washington State Public Health Laboratory using the CDC influenza A(H5) assay. Additional testing by the University of Washington identified the virus as A(H5N1).

The second patient developed conjunctivitis, and the state public health laboratory confirmed influenza A(H5) during the week ending October 31. The specimen has been shipped to CDC for additional testing.

Washington has now reported three influenza A(H5) cases in dairy workers. Human-to-human transmission of avian influenza A(H5) has not been identified in the US.

Related: Diagnostic Testing Is First Line of Defense Against H5N1

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Hospitalizations, Outpatient Visits, and Deaths

Severe disease indicators are also trending upward. Hospitals reported 8,396 patients admitted with laboratory-confirmed influenza during the week, a rate of 2.5 per 100,000 population. The cumulative hospitalization rate in FluSurv-NET is 6.0 per 100,000. The highest rate is among adults 65 and older, at 19.8 per 100,000. Among hospitalized patients with subtype information, 99.2% had A(H1N1)pdm09.

Outpatient and emergency department measures are rising as well:

• 2.8% of outpatient visits were for influenza-like illness, up from the previous week but still below the national baseline of 2.9%.
• 1.7% of emergency department visits carried an influenza discharge diagnosis, also an increase.
• Two jurisdictions reported high influenza-like illness activity, and five reported moderate activity.

Influenza accounted for 0.3% of deaths during the week, a figure that has remained stable week to week but has trended upward over the past 7 weeks. Two pediatric deaths from the 2026-2027 season were reported this week, bringing the season total to three. Three additional deaths from the 2025-2026 season were also reported, bringing that season’s total to 202.

CDC’s preliminary in-season assessment classifies severity as low across all age groups, though it may change as activity increases. The agency estimates at least 1.7 million illnesses, 25,000 hospitalizations, and 1,400 deaths so far this season.

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Forecast and Recommendations

CDC’s FluSight forecasts predict a likely national increase in both flu hospital admissions and the percentage of emergency department visits due to flu for the week ending November 21. New admissions are projected to range from 6,900 to 30,100, and emergency department visits from 1.6% to 6.7%.

CDC continues to recommend annual influenza vaccination for people 6 months and older, and urges those not yet vaccinated this season to get vaccinated now. The agency also notes that prescription antivirals should be started as early as possible, particularly for patients at higher risk for complications.

Related: New Rapid Test Detects Influenza A, B, and COVID-19 in Single Assay

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